Explosive fuse-cord

ABSTRACT

An explosive fuse-cord suitable for underwater use, comprising a core of powdered explosive material enclosed in a tubular continuous layer of hot melt waterproof adhesive composition disposed immediately around the core. The invention also includes a method of manufacturing fuse-cord in which an explosive core is fed into a tube of hot melt adhesive material as the tube is being formed and the tube is heated to effect continuity of the adhesive material.

United States Patent Turner Sept. 30, 1975 [5 EXPLOSIVE FUSE-CORD 3.349705 10/1967 Wilson 102/27 3,382,802 5/1968 Prior et 21L. 102/27 [75] Inventor: g y" 3 Turner Ardrossa 3.415.703 l2/l968 Burgess l56/320 FOREIGN PATENTS OR APPLICATIONS [73] Assignce: Imperial Chemical Industries 1 7 7 1968 v d 7 7 Limited, London England 00 Unlte mgdom .4 l0 /-7 [22] Filed: Aug. 24, 1973 Primary E.\'uminerVerlin R. Pendegrass Attorney, Agent, or FirmC1ushman, Darby & [21] Appl. No.. 391,513 Cushman [30] Foreign Application Priority Data ABSTRACT Sap]; 6 1973 U i d Ki 4135 /72 An explosive fuse-cord suitable for underwater use,

comprising a core of powdered explosive material en- [5'2] U.S. Cl. 102/27 R; 102/27 l e n a ubular continuous layer of hot melt water- [51] Int. Cl.'- C06C 5/04 pr of a h sive composition disposed immediately [58] Field of Search 102/27; 156/304, 320, 544 around the core. The invention also includes a method of manufacturing fuse-cord in which an explosive core [56] Reference Cited is fed into a tube of hot melt adhesive material as the UNITED STATES PATENTS tube is being formed and the tube is heated to effect 871.696 11/1907 Herr 102 27 commmty ofthe adhcswe mateml 1674.773 6/1928 Fritzsche 102/27 13 Claims, 2 Drawing Figures US. Patent Sept. 30,1975

H II

EXPLOSIVE FUSE-CORD This invention relates to explosive fuse'cord and to a method of manufacturing explosive fuse-cord. The invention is especially useful for providing fuse-cords for underwater use.

In one commonly used construction of explosive fuse-cord an explosive core is encased in a thin paper or plastics tube reinforced with wrapping material usually comprising one or more spun layers of textile yarns surrounded by an outer sheath of thermoplastic material. In the manufacture of cords of this construction, the thin tube is continuously formed from tape, usually longitudinal tape, which is curved around its longitudinal axis to form the tube by passing it through a die. The explosive is continuously fed from a hopper into the tube as the tube is being formed and is consolidated by passing the tube through dies to form the explosive core. Textile yarns on bobbins rotating around the tube are continuously hclically wound around the tube and the outer sheath is extruded around the yarns.

The explosive materials normally used in fuse-cords are readily desensitised by water. Thus a fuse-cord with a core of crystalline pentaerythritol tetranitrate will be insensitive to initiation by a standard detonator if the end of the cord is immersed in water for a period of time, To counteract this the explosive powder has been treated with waterproofing coating agents but these were only effective to a depth of cm of water. For use at greater water depths it was preferable to mix about I to 27: by weight of a water-gellable material, for example guar gum, with the explosive powder and this had the effect of forming a relatively impenetrable barrier of gelled material at the exposed end of the explosive core and thereby slowing the ingress of water. This treatment has not, however, been completely successful because, although the water is prevented from migrating through the end of the explosive core, we have found that it can migrate along the textile layer and attack the explosive core from the side, whereby the explosive material becomes waterlogged and insensitive.

It is an object of this invention to provide an improved water-resistant construction of explosive fusecord.

In accordance with this invention an explosive fusecord comprises a core of waterdesensitisable explosive material enclosed in a tubular continuous layer of hot melt waterproof adhesive composition disposed immediately around the core.

The hot melt adhesive composition is conveniently in the form of one or more tapes wrapped around the core and heat sealed at the edges to form a continuous tube of'adhesive composition. The'tape is conveniently provided as one or more longitudinal tapes curved along their longitudinal axes to surround the core, preferably with the edges overlapping and heat sealed at the overlapped portions. The tape preferably comprises a layer of hot melt adhesive on a supporting substrate which may conveniently be paper or synthetic plastics film. Where the fuse-cord comprises two or more supported tapes of hot melt adhesive it is preferred that the tapes should be oriented so that the substrates alternately face inwards and outwards with the edges overlapping and the adhesive material of the overlapping portions facing each other and heat sealed together.

In the completed fuse-cord, the tubular layer of hot melt adhesive is conveniently surrounded by one or more spun layers of textile materials, for example jute, cotton or synthetic plastics filament, to provide reinforcement, and the cord may have an outer extruded sheath of synthetic thermoplastics material, for example polyvinyl chloride or polyethylene, as in conventional detonating fuse-cord.

The hot melt adhesive composition preferably has a bonding temperature in the range 50 to 90C, more preferably in the range to C. It may be based on protein glue or wax but preferably it is based on cellulose ester or ether, or synthetic organic polymer, for example polyvinyl ester, polyvinyl acetal, polyamide or a terpolymer rubber consisting of ethylene and propylene terpolymerised with an unsaturated hydrocarbon such as butadiene. Especially convenient synthetic polymers are copolymers of vinyl acetate and ethylene comprising 7 to 30% vinyl acetate. The composition conveniently also comprises a tack resin, for example a coumarone-indene tack resin, a terpene tack resin or a rosin derivative such as hydrogenated rosin, dehydrogenated rosin and esters of these derivatives.

The explosive core is preferably in powder form and may, for example, comprise blackpowder in a safety fuse-cord or crystalline pentaerythritol tetranitrate in detonating cord. In detonating cord the explosive powder may be coated with a waterproofing agent, for example silicone, but for use in deep water the powder should preferably be mixed with a water-gellable material, for example guar gum or a salt of carboxymethyl cellulose.

The invention also includes a method of manufacturing an explosive fuse-cord which comprises continuously forming a tube from hot melt adhesive tape material, introducing explosive material into the tube during the formation thereof to form a continuous explosive core in the said tube and heating the tube to effect continuity of the adhesive material. The tube is preferably surrounded with reinforcing wrapping materials, for example one or more spun layers of textile materials and, if desired, an extruded sheath of synthetic thermoplastics material.

Preferably the edges of the tape are overlapped, the

overlapped portions being bonded together when the tube is heated. In a preferred method, the tube of hot melt adhesive is formed from one or more longitudinal tapes curved around their longitudinal axes and heat sealed at the edges. Where the fuse-cord is surrounded by an extruded sheath of thermoplastics material the heat from the thermoplastics material may be sufficient to melt the adhesive and it is generally convenient to use a hot melt adhesive of sufficiently low melting point to be heat sealed in this manner without the need for a separate heat sealing stage in the manufacture.

The preferred hot melt adhesive tape comprises a layer of adhesive on a supporting substrate and where two or more tapes are used they should preferably be laid with the substrates of the tapes facing alternately inwards and outwards with the edges overlapping and the adhesive material on overlapping edges in contact.

In order to illustrate the invention further, one preferred construction of a fuse-cord is hereinafter described, by way of example only, with reference to the accompanying drawings wherein FIG. 1 shows diagrammatically a length of fuse-cord with one end dissected.

FIG. 2 is a cross-section on the line Illl of FIG. 1 on a larger scale. 1

The fuse-cord has a core 11 of powdered explosive enclosed in a tube formed from twotapes 12, the edges of the tapes being overlapped and heat sealed as shown in FIG. 2. The core contains a single axial yarn 13 to assist the flow of explosive from a hopper during the fuse-cord manufacture. The tapes 12 are surrounded by a spun layer 14 and a counter-spun layer 15 of textile yarns or tapes and the textile layers are surrounded by-a sheath 16 of synthetic thermoplastics material. The tapes l2 consist of a substrate 17 with a layer of hot melt adhesive 18 thereon, one tape having the substrate facing inwards and the other with the substrate outwards.

The following specific Examples of a detonating cord of the aforedescribed construction further illustrates the invention. All parts and percentages are quoted by weight.

EXAMPLE 1 Crystalline PETN'at a charge rate of grams per metre was loaded into a tube formed from two tapes 12 consisting of a substrate 17 of Kraft paper 0.08 mm thick with a 0.13 mm thick layer of hot melt adhesive composition 18 thereon. The composition of the adhesive was 33.3% of a copolymer of 28 parts vinyl acetate and 72 parts ethylene, the melt flow index of the copolymer being 20 33.3% Staybelite (Registered Trade Mark) Ester 10, tack resin, a glycerol ester of hydrogenated wood rosin commercially available from Hercules Inc.

33.3% Paraffin wax (MP 62C) 0.1% Butylated hydroxy toluene (anti-oxidant).

The yarn 13 was 1000 denier polypropylene.

The spun layer 14 consisted of 10 yarns of 1000 denier polypropylene and the countering layer consisted of 8 similar yarns. The sheath 16 was polyvinyl chloride.

Lengths of this fuse-cord with the ends exposed propagated detonation satisfactorily after immersion under a depth of 5 metres of water for 72 hours.

EXAMPLE 2 A fuse-cord was constructed as described in Example 1 except that the composition of the hot melt adhesive was 35.0% of a copolymer of 28 parts vinyl acetate and 72 parts ethylene, the melt flow index of the copolymer being 150 35.0% Staybelite Ester 10 29.9% Paraffin wax (MP 62C) 0.1% Butylated hydroxy toluene. The fuse-cord had water resistance similar to that of Example 1.

EXAMPLE 3 A fuse-cord was constructed as described in Example 1 except that the composition of the hot melt adhesive was 35.0% of a copolymer of 24 parts vinyl acetate'and 76 parts ethylene, the melt flow index of the copolymer being 10.0% Pentalyn C (Registered Trade Mark), a pentaerythritol ester of hydrogenatedwood rosin com mercially available from Hercules Inc.

40.0% Staybelite Ester 10 14.9% Paraffin wax 0.1% Butylated hydroxy toluene.

The fuse-cord had water resistance similar to that of Example 1.

What we claim is: 1. An explosive fuse-cord comprising a core of water desensitisable explosive material surrounded by at least one layer of textile material and a tape comprising a layer of hot melt adhesive composition on a supporting substrate wrapped immediately around said core, said hot melt adhesive forming a tubular continuous layer disposed between said core of explosive material and said layer of textile material.

2. A fuse-cord as claimed in claim 1 wherein the tape is curved along its longitudinal axis to surround the core.

3. A fuse-cord as-claimed in claim 1 wherein the edges of the tape are overlapped and heat sealed at the overlapped portions.

4. A fuse-cord as claimed in claim 1 wherein the hot melt adhesive composition has a bonding temperature in the range 50 to 90C.

5. A fuse-cord as claimed in claim 4 wherein the hot melt adhesive has a bonding temperature in the range 60 to C.'

6. A fuse-cord as claimed in claim 1 wherein the hot melt adhesive composition is selected from the group consisting of protein glue, wax, cellulose ester, cellulose ether and synthetic organic polymer.

7. A fuse-cord as claimed in claim 6 wherein the hot melt adhesive composition is selected from the group consisting of polyvinyl ester, polyvinyl acetal, polyamide and a terpolymer rubber consisting of ethylene and propylene terpolymerised with an unsaturated hydrocarbon.

8. A fuse-cord as claimed in claim 7 wherein the hot melt adhesive is selected from the group consisting of a copolymer of vinyl acetate and ethylene and a terpolymer of ethylene, propylene and butadiene.

9. A fuse-cord as claimed in claim 1 wherein the hot melt adhesive composition comprises a tack resin.

10. A fuse-cord as claimed in claim 9 wherein the tack resin is selected "from the group consisting of coumaroneindene tack resin, a terpene tack resin and a rosin derivative.

11. A fuse-cord as claimed in claim 10 wherein the tack resin is selected from the group consisting of hydrogenated rosin, dehydrogenated rosin and an ester of any of the said rosins.

12. A fuse-cord as claimed in claim 11 wherein the tack resin is selected from the group consisting of a hydrogenated rosin esterified with glycerol and pentaerythritol.

13. An explosive fuse-cord comprising a core of water desensitisable explosive material surrounded by at least one layer of textile material and at least two tapes wrapped around the core, each tape comprising a layer of hot melt adhesive composition on a supporting substrate, said tapes being oriented so that the substrates alternately face inwards and outwards with edges overlapping and the adhesive material of the explosive material and said layer of textile material. 

1. AN EXPLOSIVE FUSE-CORD COMPRISING A CORE OF WATER DESENSITISABLE EXPLOSIVE MATERIAL SURROUNDED BY AT LEAST ONE LAYER OFF TEXTILE MATERIAL AND A TAPE COMPRISING ZA LAYER OF HOT MELT ADHESIVE COMPOSITION ON A SUPPORTING SUBSTRATE WRAPPED IMMEDIATELY AROUND SAID CORE, SAID HOT MELT ADHESIVE FORMING A TUBULAR CONTINUOUS LAYER DISPOSED BETWEEN SAID CORE OF EXPLOSIVE MATERIAL AND SAID LAYER OF TEXTILE MATERIAL.
 2. A fuse-cord as claimed in claim 1 wherein the tape is curved along its longitudinal axis to surround the core.
 3. A fuse-cord as claimed in claim 1 wherein the edges of the tape are overlapped and heat sealed at the overlapped portions.
 4. A fuse-cord as claimed in claim 1 wherein the hot melt adhesive composition has a bonding temperature in the range 50* to 90*C.
 5. A fuse-cord as claimed in claim 4 wherein the hot melt adhesive has a bonding temperaTure in the range 60* to 80*C.
 6. A fuse-cord as claimed in claim 1 wherein the hot melt adhesive composition is selected from the group consisting of protein glue, wax, cellulose ester, cellulose ether and synthetic organic polymer.
 7. A fuse-cord as claimed in claim 6 wherein the hot melt adhesive composition is selected from the group consisting of polyvinyl ester, polyvinyl acetal, polyamide and a terpolymer rubber consisting of ethylene and propylene terpolymerised with an unsaturated hydrocarbon.
 8. A fuse-cord as claimed in claim 7 wherein the hot melt adhesive is selected from the group consisting of a copolymer of vinyl acetate and ethylene and a terpolymer of ethylene, propylene and butadiene.
 9. A fuse-cord as claimed in claim 1 wherein the hot melt adhesive composition comprises a tack resin.
 10. A fuse-cord as claimed in claim 9 wherein the tack resin is selected from the group consisting of coumaroneindene tack resin, a terpene tack resin and a rosin derivative.
 11. A fuse-cord as claimed in claim 10 wherein the tack resin is selected from the group consisting of hydrogenated rosin, dehydrogenated rosin and an ester of any of the said rosins.
 12. A fuse-cord as claimed in claim 11 wherein the tack resin is selected from the group consisting of a hydrogenated rosin esterified with glycerol and pentaerythritol.
 13. An explosive fuse-cord comprising a core of water desensitisable explosive material surrounded by at least one layer of textile material and at least two tapes wrapped around the core, each tape comprising a layer of hot melt adhesive composition on a supporting substrate, said tapes being oriented so that the substrates alternately face inwards and outwards with edges overlapping and the adhesive material of the overlapping portions facing each other and heat sealed together to form a tubular continuous layer of hot melt adhesive composition disposed between said core of explosive material and said layer of textile material. 